Driving key



Gil

Patented Sept. 25, 1928.

UNITED STATES MAX SKLOVSKY, OF MOLINE, ILLINOIS, `ASSIGNOR TO DEERE & COMPANY, OF

ILLINOIS, A CORPORATION OF ILLINOIS.

PATENT OFFICE.

DRIVING KEY.

The present invention relatesl to driving keys, such as are used for coupling together a shaftand fly-wheel, a shaft and belt pulley. and other like rotating elements.

The primary object of the invention is to provide an improved construction of safety driving key designed to fracture at a predetermined stress and thus prevent in]ury to either the driving or driven element, such as might result through the creation of an abnormal momentum, inertia shock, overload, etc. This type of key has general utility in practically all classes`of machinery where such safety feature is desired, represented for example by shop machinery, hay presses, bull-dozers, internal combustion engines etc. The present improvements have been devised to the end of providing a key which will have more 4certainty in its release function viz: a key wherein the point of failure for effecting the safety release can be predetermined within very close limits with maximum certainty.

Referring to the accompanying drawing illustrating my invention: n

Figure 1 is an elevational v iew illustrating a typical use of my invention for keying a shaft and iy-wheel together.

Figure 2 is a perspective view of the key.

Figure 3 is a similar view ofone of the quarter sections of the key after fracture has occurred.

Figure 4 is a sectional View on a larger scale, illustrating the seating of the key iii the key ways of the shaft and {1y-wheel huh.

Figure 5 is a similar view illustrating the planes of fracture and the initial movement of the key sections in the failure of the key, and

Figure 6 is a similar view illustrating the nesting of the key sections after failure.

The shaft 7 and fly-Wheel 8, chosen merely for exeniplifying typical driving and driven elements, have rectangular key seats .or key ways 9 and 10 formed therein, ex-

tending longitudinally of the shaft. The present key consists of a bar 12 of square cross section having a bore 13 extending entirely through its length. At the outer end of the key, or if desired, at both ends thereof a threaded socket 14 is formed in the bore for receiving any correspondingly threaded member serving temporarily as a tool for inserting or removing the key. This threaded socket is of particular advantage for removing the key, as by screwing a bolt or other threaded member into the socket 14, a secure grip may be had on the key for pulling the same. Where the key is to be held in the key ways 9 and 10 by a drive fit, it is formed with a slight taper. Where the hub 8 of the outer rotating element is split for clamping the key, or where other means is provided for holding the key in place, the latter can be constructed of uniform thickness throughout. The provisionof the bore 13 forms relatively thin side walls, Awhich side walls are the points at which failure of the key occurs. Thus, by varying'the diameter of this bore the breaking stress of the particularikey can be predetermined as desired. It will be noted that the bore extends longitudinally through the key so that the axis of the bore is substantially in the peripheral plane of the shaft 7.

In the construction of, the key it is given a brittle tempering so that its failure will be more iii the nature of a fracture or collapse of these'side walls rather than a shearing of the key. The key may have any desired metallic composition and may be given any desired heat treatment to obtain this brittle characteristic. For the purpose of teaching the art one method of constructing these keys I may remark that for one particular duty, for which I have successfully used the keys, I have constructed them ot' 20-30 carbon steel which is carbonized to the brittle point so that the key will crush quickly when the maximum resistance is passed. This failure of the key by fracture enables the collapsing point to be predeter- 4mined within very close limits with maximum certainty, whichis a desideratum not possible iii the case of a key failing solely by shear.

B v making the key hollow and of substantially symmetrical cross section with the axis of the bore positioned approximately in the peripheral plane of the shaft 7 the fracture is made to occur in two planes substantially at right angles to each other, so that upon failure the key breaks into four quarter sections. By `collapsing' in this manneri the key sections are caused to nest with each other whereby the release between the two rotating elements is complete so that the element having the high inertia or momentum has free rotation instantly relative to the other element. Such nesting of the MOLINE,

key sections avoids any tendency of these sections chewing off the corners of the key ways in the resulting inde ndent rotation ,of the driving and driven e ements.

Figure 5 illustrates the failure of the key in its two transverse planes and the initial movement of the broken ke sections upon such failure. The two sections at one side of the key are tipped inwardly by the breaking stresses and by the initial independent movement between the driving and driven elements, so that the inner tipped section is caused to rock over the nest with the adjacent inner section and the outer tipped y section is similarly rocked over and caused to nest with its adjacent outer section. The tipped sections thus assume the illustrated in Figure 6, nesting wlth their adjacent sections, and permitting independent rotation of the drivin and driven elements with minimum possi ility of these key sections striking and chewing off the corners of the key ways in such jindependent rotation.

What I claim as my invention and desire to secure b Letters Patent, is-

1. A sa ety driving key of the class described consisting of a hollow ybar of sub-y stantially symmetrical, uniform cross-sectional area from end to end and composed of a metal which will fracture in'its failure under'excessive stress.

2. A safety driving key of the class described consisting of a hollow bar of rectangular cross section.

3. A safety driving key for the -use described consistin of a heat treated hollow bar designed to racture at a predetermined stress.

4. A safety driving key for they use described consisting of a bar having a longitudinal bore therethrough leaving relatively thin wall sections designed to fracture in two planes upon the subjection of said key to a predetermined stress.

5. A safety driving key for reception in longitudinally extending key ways of two rotating elements, consisting of a bar of sitions substantially square cross section having a bore extending longitudinall thereof from end to end, said bar being heat treated to have a brittle characteristic for fracture upon the subjection of said key to a given stress.

6. A safety driving key for reception in longitudinally extending key ways of two rotating elements, consisting of a bar of substantially square cross section having al central bore extending longitudinally of the same from end to end thereof, said bar being composed of carbon steel carbonized to the brittle point, whereby said bar will be caused to-collapse in two planes u on the subjection thereof to a predetermine stress.

7. The combination/with two concentric rotating elements having longitudinally extending key ways in their engaging surfaces, of a safety driving key engaging in said key ways for releasably coupllng said.

elements together, said key consisting of a hollow metallic bar, of substantially rectangular cross section, having a relatively brittle temper for fracture under predetermined stress. w

8. The combination with two concentric rotating elements having longitudinall extending key ways in their engaging sur aces, of a driving key engaging in said key ways and comprising a threaded socket at one end for the reception of a threaded member utilized for drawing the same.

9. The combination with two concentric rotating elements having longitudinal] extending key ways in their engaging sur aces, of a safety driving key engaging in said key ways for coupling said elements together, said key consisting of a bar of substantially square cross section having a bore extending longitudinally through the same, said bar having a relatively brittle temper for fracture upon the subjection thereof to a predetermined stress, and a threaded.

socket in one end of said bore for the reception of a threaded member utillzed for drawing the key.

MAX SKLOVSKY. 

